Preheat the oven to 350 degrees. Line a 9-inch square pan with a foil or parchment. Spray the parchment with non-stick spray (I use Baker's Joy), or lightly grease with butter.
Melt the butter and chocolate together in a small pan over medium-low heat. When melted, remove from heat and let cool slightly.
In a large bowl, beat the eggs, sugar, crushed lavender, and vanilla until mixed. Add in melted butter and chocolate and mix until incorporated. Then add walnuts (if using) and then the flour and salt. Mix until combined smoothly. Empty bowl into prepared 9-inch pan, smooth the top. Sprinkle a light dusting of vanilla salt over the top.
Bake 25 - 30 minutes until a baking tester comes out mostly clean. Better to slightly underbake so as not to dry out. They will continue cooking a bit as they cool.
Store tightly covered in foil or on a plate in a cake stand, they will last 2-3 days on the counter.
Put the half the maldon salt in a glass jar (I use a small mason jar). Tuck in two vanilla bean pods and put the rest of the salt in the jar. Let sit a minimum of 5 days.
Put several spoonfuls of the vanilla scented maldon salt in a mortar and pestle (or spice grinder)and grind into smaller salt crytals. Keep in a clean, dry spice container in a dark, cool, place.
I generally only grind as much as I might need for each recipe.